@Aron : yes, I know what you meant.  What I'm questioning - and it may not be an issue - is how well that would hold up in an environment that is enclosed and sitting at say 85-100C.  I just don't know if that presents an issue.

Anyway, I have thought a bit about it as it is basically the same problem as how to support a "thin" telescope mirror, but with *much* wider tolerances.

the x/y carriage is made out of printed ABS, as well as the extruder for those of us that upgraded to one of the lawsy versions which *SHOULD* be OEM equipment. so im inclined to think that with sufficient engineering and high infill, the platform would work. but i would also share your concern that the plastic might get soft enough, or expand enough to move the build plate during a long print.

best option is probably to either make friends with a good welder and buy him a case of beer to TIG you up an aluminum platform out of stock aluminum profiles, or pony up the cash for the official solution.

Anyway, I have thought a bit about it as it is basically the same problem as how to support a "thin" telescope mirror, but with *much* wider tolerances.

Anyone 3D print a platform, which attaches to the rails and z rod?

What I wasn't sure about, though, is how a printed bed would perform in a heated enclosure.  I get the idea of insulating the interface between the bed itself (glass, aluminum, etc.) from heat.  But would the structure itself or it's ability to be rigid suffer in a very warm enclosure, one that would be warm enough to keep large prints from warping?

I think 45$ is too expensive for the new SD2 aluminum platform, especially considering that my aluminum build plate seems slightly warped and needs replacing as well. 

-Aron